Worm gear

from Wikipedia, the free encyclopedia

In optics and precision mechanics, a worm gear is understood to be a tube that is adjustable in length with the help of a thread and which allows, for example, a lens or mirror system to be moved on the optical axis . This is especially necessary for setting the distance (setting the image sharpness).

In general mechanics, worm flights are one of several ways of converting a rotating movement, such as a servo or stepper motor, into a translational movement, i.e. a shift. Here, however, mostly no hollow bodies (tubes), but precision spindles are used as screw gears .

construction

A worm gear is a helical gear of a fixed outer shell, for example, the connecting thread or bayonet carrying a camera, a thread located in the interior, which can be rotated by an externally accessible ring and a front cover part with a further terminal possibility (thread, Receptacle, bayonet) that moves back and forth in the longitudinal axis when the thread is turned. By turning the actuating ring, the total length of the worm thread changes steplessly between a minimum and maximum value depending on the design.

application

Snail gears are mainly used in photography and astronomy , where they are used to adjust the distance (focus). In mechanics , they enable precise, sometimes computer-controlled, fine movements.

Cameras

With photo cameras they are built into the lens and with modern digital cameras they are usually coupled with the automatic rangefinder . In system and SLR cameras and older models, the worm gear is controlled by the rotatable distance or focus scale and changes the overall length of the lens (see image distance): if you set a short distance, part of the lens moves forward (from the image plane away from the camera). Newer lenses with internal focussing remain unchanged in length or can appear to be shorter, since the distance setting is done by moving individual lens groups within the lens.

Telescopes

In astronomical telescopes , the eyepiece is often equipped with a worm gear. The focus is brought about by turning the eyepiece - but in contrast to the camera lens, the eyepiece is shifted here: namely, at close-up by a few millimeters away from the telescope lens . The longer the focal length of the telescope, the longer the focus range .

With large observatory telescopes and older or simple amateur telescopes , the adjustment mechanism is usually not a worm, but a rack with a rotary knob.

In the case of binoculars , the distance is adjusted using the central drive connected to a rack, but the right eyepiece has a worm gear which enables diopter compensation for different eyes.

Other uses

Furthermore, screw flights are used in many forms wherever precise feed movements are required - for example in measurement technology , in precision mechanics , in mechanical engineering and elsewhere. These worm flights are often provided with mechanical or electrical drives.

literature

  • Max Haase: Handbook of scientific and applied photography. Supplementary work, first volume, Springer Verlag, Vienna 1943.
  • Josef Reiner: Basics of ophthalmic optics. 1st edition, 2002, ISBN 978-383-112767-2 .